1) Field of the Invention
The present invention relates to a technology to perform corrections for color difference and position difference in a color laser printer.
2) Description of the Related Art
In general, a color electrophotographic printer has peripherals for each of a plurality of photosensitive drums and sequentially transfers images of cyan, magenta, yellow, and black on each photosensitive drum onto a transfer paper to obtain a color image. As disclosed in Japanese Patent Application Laid-open Publication No. 07-199576, a technique for correcting color difference is well known for the color electrophotographic printer
In the conventional technique, fluctuated image data due to mechanical fluctuations is measured on the transfer belt to obtain color difference data, based on which correction timing data for enabling a color-difference-corrected optical writing is created. Based on the correction timing data, an optical writing device is operated to perform a writing.
However, the belt speed changes due to a deviation of two transfer belt rollers, and even if the angular velocity of rotation is constant, the transport speed changes resulting from a change in thickness in each portion of the transfer belt. The transport speed of the transfer belt is unique to each transfer belt unit. Therefore, when the transfer belt unit is replaced, since an error such as color difference takes place, the quality of the output color image may deteriorate, as compared with the quality before replacing the transfer belt unit.